Heretofore, many devices of high sensitivity have been developed for particle size measurements. These either rely on direct dimensional measurement; sieving and microscopy or depend on physical response, i.e. electrozone, various light beam interference techniques or sedimentation. Most of these techniques are either time consuming, require expensive equipment or are capable of analysing small samples only. In addition, the majority are not suitable for on-line monitoring. This is an important drawback as in the manufacture, for example, of industrial powders as diverse as paint pigments, cement and photocopier toner, there is a requirement to control tightly the particle size distribution. An on-line capability allows immediate readjustment of the process parameters that control the particle size if and when required.
A recent review of the most widely used techniques for particle size analysis has been presented in a publication by T. Allen, "Particle Size Measurement", Fourth edition, 1990 (Chapman and Hall: London).
The aim of the present invention is to provide a new and improved particle size distribution analyser.
According to the present invention there is provided a particle size analyser comprising a horizontally held close-coiled helical spring, partly filled with the powder under test, means to stretch the spring along its length and means to measure its corresponding extension, means to vibrate the spring in a direction normal to its main axis at selected frequency and amplitude of vibration, and means to direct the discharged powder from the spring coils into a container for mass measurement.